Therefore Jonny has been carrying out a series of tests on F-15-0 motors in order to get performance data that can then be used to more accurately predict, model and achieve a propulsive landing. The video below is the 4th and final test, data from each test can also be downloaded in the video description.
Head over to Twitter to find out more on Joes’s landing legs and grid fin design!
Video Caption: After building a ground-up simulation of the vehicle’s behavior under thrust, I re-tuned the stability algorithm to the inertia I calculated from the results of a bifilar pendulum test. The calculation was incorrect, due to an extra set of parentheses used, and the algorithm was then tuned to the incorrect vehicle inertia. The calculated inertia was much smaller than it should have been, so the simulation predicted a vehicle requiring less control authority, hence the loose oscillation during the test. The error was found soon after.
Video Caption: Once the error in the inertia calculation of the Series B Hold Down was found, a second bifilar pendulum test was conducted with newly added landing legs and grid fins to obtain an updated measurement. The vehicle was once again tuned in the simulation, the values were set in the flight software, and the test was conducted.
A slight oscillation can be seen during the test. The cause is unconfirmed, but is likely due to the following factors. A changing CG during the burn, a slightly loose TVC mount due to ascent and landing motors being loaded, or inconsistencies in the propellant causing small non-axial moments on the vehicle. There are other potential factors, but these are the most likely.
This test passes overall, and with a sufficiently accurate tuning(for the flight profile), focus will now be set on aerodynamic testing and flight software work.
In this video, Joe goes over the recent work on his launch pad and his continued tuning of his control algorithms for thrust vector control.
Video Caption: This test was not intended to(and does not) feature a fully stable vehicle or tuning. The purpose of Series A is to gather high resolution data from the flight computer in order to build an accurate offline model of the vehicle, and its response to a given TVC correction value. The vehicle aimed to keep one axis steady, while cycling through a 10 degree offset in the set-point on the other axis, roughly halfway through the burn. Using the offline model, I can tune the stabilization algorithm without running complicated and expensive tests, saving time in the process. A TVC Series B test will be conducted after thorough offline verification of the ideal tuning is ready, likely within two weeks.
Joe Barnard has made significant progress on his in-house designed and built Signal flight computer. This computer will support his efforts in trying to propulsively land a hobby rocket. Joe does a much better explanation of the system in the video below, but if you are interested check out the Signal Avionics web page over at BPS.
Video Caption: This is the 3rd attempt at fitting everything onto the flight computer efficiently. Probably won’t be the last. This is a large chunk of the design process, but there’s much more to do before the board is finalized.